Temperature indicator



Dec. 31,1935. 'GECAMILLI 2,026,375 r TEMPERATURE INDICATOR Filed May 27, 1935 Inventor: Guglielmo Camilli,

H is Attorney Patented 31, 1935 UNITED STATES,

' TEMPERATURE INDICATOR Guglielmo Camilli, Pittsfielil, Mass assignor to General Electric Company, a corporation of New York Application May 27, 1935, Serial No. 23,600 v3 Claims. (01. 73-52)- My invention relates to temperature indicators for liquid-immersed electrical apparatus such as transformers and reactors. The'temperature of the internal parts of a transformer or reactor in- 5 creases as its load or current is increased and the maximum fsafe load or current is limited by the maximum safe, internal temperature. It is therefore often desirable to be able to determine quickly and conveniently the temperature of the 10 hottest part of the apparatus. When the apparatus is not in operation, it will of course assume the same temperature'as that of the surrounding air. When the apparatus is. in operation, how- 'ever, its electrical and magnetic losses appear 15 as heat and its temperature rises.- In apparatus of the liquid-immersed type the heat is absorbed,

from the apparatus by the surrounding liquid which carries it to. the casing containing the apparatus where it is dissipated. The internal temperature of the apparatus is of course higher than that ofthe surrounding liquid except when no load is being carried and the difference between the temperatures of the liquid and the apparatus is approximately a function of the load or cur- 25 rent carried by the apparatus.

The general object of the invention, therefore, is to provide an improved temperature indicator arranged to respond to the temperature of the liquid and to the effect of the current carried by 0 the apparatus to indicate the internal temperature of the apparatus.

The invention will be better understood from the following description taken inconnectlon with the accompanying drawing in which Fig. 1

35 is a view partly in section of a temperature indicator constructed in accordance with the in= vention; Fig. 2 is a view of a liquid-immersed transformer provided with the temperature indicator shown in Fig. 1; and Figs. 3 and 4 are ex- 40 planatory, diagrammatic views. Like reference characters indicate similar parts in the different figures of the drawing.

The transformer Ill shown in Fig. 2 is immersed in a body of insulating liquid N in a 45 metal casing l2.

shown more in detail in Fig. 1, is mounted onthe cover of the casing I land connected to a temperature indicating instrument Mmountedon the wall of the casing l2. The temperature indicator I 3 in- 50 cludes a switch casing l5 having a base 16' bolted to the cover of the transformer casing l2. A

resistance tube I1 is suspended in the insulating liquid II by a support l8 depending from the base l8 of the switch casing. A temperature responsive element I9 is disposed within the resist- A temperature indicator l3,.

' ance tube I! and is therefore thermally close to the tube ll so that its temperature will always follow that of the tube. The temperature re-' sponsive element I 9 is connected through the support l8 and the switch casing l5 to the indi- 5 eating instrument M by a suitable connection. The temperature responsive .element l9 may be of any suitable type which will control the indicating instrument It and cause it to indicate the temperature of the resistance tube l1. As 10 indicated in Fig. 4 the temperature responsive element I9 is the usual form of thermometer bulb connected by a capillary tube 20 to the indicating instrument l4. As indicated in Fig. 3, the temperature responsive element I9 is a resistor of the type which changes in its resistance in response to changes in its temperature. This resistor I 9 is connected by conductors to the indicating instrument M which is of course ar-' ranged to indicate the temperature .correspond- 20 ing to the resistance of the resistor IS.

The primary winding of a current transformer 2| is connected in series with one of the leads of the main transformer i II and the secondary winding of this'current transformer 2| is connected to the terminals 22 and 23 of the resistance tube IT. The terminals 22 and 23 ofthe tube I! are also connected to a switch 24 in the switch casing IS. The temperature responsive element '19 is closely surrounded by the resistance tube so that it will always have the same temperature and will always cause this temperature to be indicated by the indicating instrument Hi. If there is no load on the transformer, then the transformer and the liquid ll surrounding it will be at the same temperature'and the temperature responsive element will respond to this temperature and cause it to be indicated by the instrument Hi. If the transformer is carrying a load, then there will be a current in the primary winding 40 of the winding of the main transformer In. The

resistance tube I! is preferably formed of some suitable non-magnetic material'such as stainless steel so that its temperature will not be affected by induction from the adjacent apparatus. This resistance tube ll closely surrounds the temperature responsive element l9 and thus affords good mechanical protection for the temperature responsive element.

It is sometimes desirable to know the temperature of the liquid II as well as the internal temperature of the transformer in. If the switch 24 is closed, it completes a short circuit across the resistance tube I! so that any current from the current transformer 2| will flow through the switch rather than through the resistance tube. With this switch 24 closed, therefore, the instrument I4 will indicate the temperature of the liquid II even though a load is being carried by the main transformer ID.

The invention has been explained by describing and illustrating a particular form and application of the invention but it will be apparent that changes may be made without departing from the spirit of the invention and the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The .combination with electrical apparatus immersed in an insulating liquid, of a temperature indicator including a resistance immersed in said liquid and connected to carry a current proportional to that in said apparatus, a temperature responsive element thermally close to said resistance, a temperature indicating instrument connected to said temperature responsive element, and a switch connected to short circuit said resistance.

2. The combination with electrical apparatus 5 immersed in an insulating liquid within a casing, of a temperature indicator including a resistance immersed in said liquid and connected to carry a current proportional to that in said apparatus,

a temperature responsive element thermally close to said resistance, a switch casing mounted on said apparatus casing, a temperature indieating instrument connected through said switch casing to said temperature responsive element, and a switch in said switch casing connected to short circuit said resistance. r 3. The combination with electrical apparatus 1 immersed in an insulating liquid, of a temperature indicator including a resistance tube immersed in said liquid and connected to carry a current proportional to that in said apparatus, a temperature responsive element within said resistance tube and spaced therefrom, a temperature indicating instrument connected to said temperature responsive element, and a switch connected to short circuit said resistance tube.

GUGLIELMO CAMILLI. 

